Today we had a short 55-kilometer (34-mile) transit to the northern part of Alfonso Basin, in the greater La Paz embayment off southern Baja California. We visited a site that our collaborator Juan Carlos Herguera has been sampling for the past 15 years. He has taken numerous types of sediment cores from different ships, but has never viewed the seafloor at this study site as we were able to do today with the remotely operated vehicle's (ROV) video cameras.

A number of dolphins swimming in our bow wave provided the in-transit entertainment this morning.

The bay is around 450 meters (1,475 feet) deep and bathed at depth by extremely oxygen-depleted waters that are part of the broad oxygen minimum zone (OMZ) beginning at 100 meters (328 feet) deep and extending all the way to the seafloor. During today's dive, we measured oxygen concentrations as low as 0.04 milliliters per liter at 400 meters (1,300 feet). Even with such low oxygen in the surrounding seawater, we observed a number of fish, squid, and shrimp actively swimming within this oxygen-depleted benthic boundary layer. However, we didn't see any epifaunal macro-organisms, the large animals that live on the seafloor.

Conductivity, temperature, and depth (CTD) profile for our dive site in Alfonso Basin with depth increasing along the left side of the plot. The green trace is the oxygen concentration in milliliters per liter (ml/l). The oxygen minimum zone is between 100 to 420 meters (330 to 1,400 feet) where oxygen values are less than 0.5 ml/l.

We ran two 200-meter-long (650-foot-long) video transects to characterize the seafloor and confirm that we weren't missing some of these important organisms. Sure enough, we didn't find any (no brittle stars, sea cucumbers, or worms), not even the traces of benthic organisms that we commonly see on the seafloor such as tracks, trails, and burrows. The desert-like appearance at the bottom of this small basin was in a way analogous to the dry, terrestrial landscape we could see surrounding the bay. The contrast with the shallow surface ocean layer teeming with life can only be explained by the great hostility of these oxygen-depleted waters to most forms of life we know in the deep.

However, we found a number of large bacterial mats. These large white, orange, and gray mats may indicate the site of dead and decaying organisms on the seafloor. Since there are no epifaunal macro-organisms to scavenge the dead organisms, the bacteria and small, microscopic infaunal species (microorganisms that burrow into the seafloor or seafloor deposits) may have these nutrient-rich food falls to themselves.

Close-up frame grab of a large, white bacterial mat. The two red dots are lasers shining from the ROV. At 29 centimeters (11.4 inches) apart, these lasers help the scientists scale objects in the video images.

We collected six vibracores and a number of push cores to compare with Juan Carlos's historical samples. These samples will further help to characterize the sedimentation of this basin over time and how consistent these patterns are over a few thousand meters distance. One of the vibracores we collected today was 193 centimeters (76 inches) long and will probably illustrate conditions in this basin for the past 7,000 years.

The biologists processed four push cores that were taken from large white bacterial mats. We rinsed the top 10 centimeters of each core and studied the epifaunal organisms under the microscope. We found filamentous bacteria, nematodes, a huge diversity of forams, and at least three different species of pteropods.

The ROV's manipulator arm taking a push core sample in the middle of a large white bacterial mat.

This low-oxygen seafloor in the Gulf of California might give us a glimpse into the future of our coastal oceans. Many studies have determined that with the increase of carbon dioxide in surface waters, oxygen minimum zones are expanding in coastal areas. If this trend persists, scientists will likely encounter more and more of these "dead zones" on the seafloor where very few organisms can survive.

—Kris Walz

Paulino Perez Gonzalez is our shoreside support when the R/V Western Flyer is in port in La Paz. He has been a valuable assistant to the crew members who prepare the ship for the next leg of the expedition while we are in port. In addition, he studied marine biology and leads tours of marine mammals along the Pacific coast from Baja to Alaska.

The R/V Western Flyer is a small water-plane area twin hull (SWATH) oceanographic research vessel measuring 35.6 meters long and 16.2 meters wide. It was designed and constructed for MBARI to serve as the support vessel for ROV operations. Her missions include the Monterey Bay as well as extended cruises to Hawaii, Gulf of California and the Pacific Northwest.

ROV Doc Ricketts

ROV Doc Ricketts is MBARI's next generation ROV. The system breaks new ground in providing an integrated unmanned submersible research platform, with many powerful features providing efficient, reliable and precise sampling and data collection in a wide range of missions.

Heat-flow probe

MBARI's heat-flow probe is mounted on the side of the ROV Doc Ricketts inside the vertical stainless steel box. This both protects the delicate probe and provide the track so that the probe can be inserted into the sediment along a totally straight path. The probe contains five high precision platinum sensors which are used to measure the vertical temperature gradient in the sediments. This gradient along with some knowledge of the heat capacity of the sediment allows scientists to calculate the rate of heat loss from the sediments into the ocean.

In situ gas sampler

These are devices that are used to collect and sample gaseous gases bubbling out of seafloor vents. The way they work is by having small pressure vials (like tiny scuba tanks) from which the air is pumped out with a vacuum pump on the surface and sealed with the valve. On the bottom gases are captured underneath an overturned funnel so that a large gas headspace is developed. Then the value on the pressure vial is opened, gas is sucked into the vial, and the vial's value is re-closed. This way a sample of the gas at the high seafloor pressures is recovered.

In situ ultraviolet spectrophotometer (ISUS)

The ISUS is a sensor used to measure concentrations of dissolved chemicals directly from their Ultraviolet Absorption Spectrum. A variety of chemicals absorb light in the UV and each of these chemicals has a unique absorption spectrum. We can determine the concentration of these chemicals directly, with no chemical manipulation, by measuring the absorption spectrum of seawater in the UV and then deconvolving the spectra to yield the concentration of each component. ISUS has been used to determine nitrate concentrations while deployed on CTD/Rosette profilers, undulating towed vehicles such as a SeaSoar or SeaSciences Acrobat, and on deep-sea moorings. It has also been used to measure sulfide flux from cold seeps in Monterey Bay while deployed on the ROV Ventana.

Push cores

A push-core looks like a clear plastic tube with a rubber handle on one end. Just as its name implies, the push core is pushed down into loose sediment using the ROV's manipulator arm. As the sediment fills up the core, water exits out the top through one-way valves. When the core is pulled up again, these valves close, which (most of the time) keeps the sediment from sliding out of the core tube. When we bring these cores back to the surface, we typically look for living animals and organic material in the sediments.

Vibracores

Vibracoring is a common technique used to obtain samples from water-saturated sediment. These corers work by attaching a motor that induces high frequency vibrations in the core liner that in turn liquefies the sediment directly around the core cutter, enabling it to pass through the sediment with little resistance.

Gravity corer

Device lowered off the ship to the seafloor on a wire which consists of a long tube that extends below a moderately heavy weight. When the device encounters the bottom, the weight forces the tube into the sediments. When it is pulled out of the bottom the tube will contain a sediment sample (i.e., core) of the upper layers of the ocean floor.

Crew

R/V Western Flyer

Ian Young
Master

George Gunther
First Mate

Matt Noyes
Chief Engineer

Cole Davis
Second Mate

Lance Wardle
First Engineer

Shaun Summer
Relief First Engineer

Olin Jordan
Oiler

Craig Heihn
Relief Deckhand

Jason Jordan
Relief Deckhand

Dan Chamberlain
Electronics Officer

Eric Fitzgerald
Steward

ROV Doc Ricketts

Knute Brekke
Chief ROV Pilot

Mark Talkovic
Senior ROV Pilot

Randy Prickett
Senior ROV Pilot

Bryan Schaefer
ROV Pilot/Technician

Eric Martin
ROV Pilot/Technician

Leg 6 Research Team

Charlie Paull
Chief Scientist
MBARI

Charlie Paull has been a marine geologist and geochemical stratigrapher at MBARI since January 1999. The central theme of Charlie's work involves investigating the fluxes of fluids and gases through continental margins. Over the past decade his primary focus has been gas hydrate research on the Blake Ridge gas hydrate field on the continental rise off of southeastern North America. Assessing the global distribution of gas hydrate and interstitial gas is a continuing interest as well as the development of new techniques to detect the presence of gas hydrate in marine sediments. Charlie's other ongoing work is focused on the geology associated with seafloor seepage sites, including investigating the deposits associated with chemosynthetic communities, determining the processes that occur at the methane-sulfate boundary, and understanding the origin of pockmarks and other potential seafloor fluid venting sites.

Bob Vrijenhoek
Chief Scientist
MBARI

Bob Vrijenhoek leads MBARI's molecular ecology group, which focuses on using molecular tools to examine population structure and evolutionary relationships. His group is working on a number of projects studying gene flow and barriers to dispersal of deep-sea invertebrates associated with cold seeps in the Monterey Bay and hydrothermal vents at ridge sites throughout the world. The group also studies DNA sequence information from bacterial symbionts to examine their evolutionary relationships with their hosts and infer possible modes of transmission.

Krystle Anderson
Research Technician
MBARI

Krystle Anderson is a research technician working for Charlie Paull in the Continental Margins Lab. Krystle's background is primarily in the acquisition and processing of seafloor mapping data. She came from the California State University, Monterey Bay Seafloor Mapping Lab where she obtained her data processing and Geographic Information System (GIS) skills. Krystle spends a majority of her time processing and creating high-resolution maps of multibeam data collected from the mapping AUV. The high-resolution maps Krystle helps create will then be used to aid navigation for the ROV to explore particular areas of interest. On this expedition Krystle will assist with running the GIS system, and processing and cataloguing sediment samples and vibracores. This is Krystle's second research expedition with MBARI and she is very excited to be involved in this expedition.

Roberto Gwiazda
Research Specialist
MBARI

Roberto is a geochemist by training. His interests lie at the intersection of marine geology and sediment and water chemistry. During cruises Roberto operates a custom-built, portable chemistry lab that includes a complete set of analytical platforms for measurements of fluids and gases. On this expedition, Roberto will be responsible for analytical measurements of pore water chemistry on samples taken from sediment cores. He will also be in charge of collecting gas samples emanating from fluid vents and performing hydrocarbon analyses on dissolved gases collected from pore waters, from gas vents and from seawater.

Josh Plant
Research Technician
MBARI

As a member of Ken Johnson's Chemical Sensor team, Josh spends much of his time analyzing chemical data collected from instruments developed by the group. One of the main goals of these measurements is to decipher how biology affects the cycling of the measured chemicals. In the Gulf of California Josh will be measuring the distribution of sulfide in waters overlying cold seep communities as well as helping to process biological samples for the molecular ecology group. Sulfide is one of the energy sources which fuels seep ecosystems. When not at work Josh spends much of his time on or near the ocean, fishing and hiking, or working in his garden.

Kris Walz
Research Assistant
MBARI

Kris Walz works with the Midwater Ecology team at MBARI where she studies pelagic animals and their distributions using horizontal video transects collected from midwater time-series dives (1993 to present) in Monterey Bay. She joins the science teams on this leg of the Gulf of California expedition to assist with their research by recording and annotating video during the ROV dives, and processing biological samples collected from the ROV.

Brian specializes in sedimentary processes and stratigraphy, integrating insights gleaned from seafloor rock and sediment samples with information from remote-mapping products, such as close-up photographs of the seafloor, high-resolution bathymetric maps, and seismic-reflection profiles. His recent studies have focused on how sediment moves from the land to the deep sea, processes controlling submarine landslides, saltwater intrusion into coastal aquifer systems, marine pollution, seafloor habitats, and the Cenozoic history of the Arctic Ocean.

Juan Carlos Herguera
Collaborator
CICESE

Juan Carlos is interested in the history of past oceans, how changes in climate and ocean circulation contribute to the ecology and biogeochemical cycling sustained by coastal environments in the California Current and the Gulf of California regions. During this cruise he will be involved in sampling benthic foraminifera to help characterize their genomic information, and, through their stable isotopic and metal compositions, to understand how these geochemical markers reflect their ambient conditions. He will further use planktonic foraminifera for dating the deep-sea cores with radiocarbon techniques, which hold important clues on the tectonic rupturing rhythm along the boundary between the North American and Pacific plates. He is fascinated by these new observation windows opened up by the ROV deployed from the Western Flyer, making possible the discovery of new vent environments along these fractured boundaries and the chemosynthetic oasis sustained by these leaky enclaves that connect the deep ocean with the lower crust and mantle dynamics.

Mary's interests focus on using microbiota (primarily foraminifera but also pollen) to investigate marine sediment transport, geohazards (faulting, landslides and paleotsunamis), climate change, and the pathways and impact of invasive species introductions using sediment records and molecular analysis techniques. She also uses foraminifera in biomonitoring marine pollution sites and carbon-14 chronostratigraphy—the study of the age of rock layers in relation to time.

Greg Rouse
Professor
Scripps Institution of Oceanography

Greg uses morphological and molecular data to assess relationships among animals. His morphological studies range across various adult and larval anatomies using transmission and scanning electron microscopy as well as confocal laser scanning microscopy. This is combined with molecular (DNA sequence) data to infer phylogenetic relationships and hence evolutionary patterns. His research interests include the biodiversity and distribution of hydrothermal vent animals from the eastern and western Pacific, as well as those from methane seeps in the eastern Pacific. This often involves the discovery and naming of new species of animals.

Sigrid Katz
Postdoctoral Fellow
Scripps Institution of Oceanography

Sigrid is a postdoc at Scripps in Greg Rouse's lab. Sigrid received her Ph.D. in Austria working on Osedax from whale falls and has continued this work during her postdoc. She is interested in symbioses, vent organisms, and their relationships.